Planar lipid bilayer technique

Pharmacological Methods and Results. The data upon which the following discussion is based were accumulated using three techniques mouse bioassay, displacement of radiolabelled saxitoxin from rabbit brain membranes, and blockage of sodium conductance through rat sarcolemmal sodium channels incorporated into planar lipid bilayers. The results are summarized in Figures 11 and 12. 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Among the different available preparation techniques, direct formation of planar lipid bilayers from unilamellar vesicles is the most widespread method for obtaining solvent-free model membranes providing the required platform to study adsorption of proteins. 

The QCM has added valuable information about the mechanism of vesicle fusion on a surface. For instance, Kasemo and coworkers have unraveled the formation of planar lipid bilayers on Si02 and glassy surfaces by means of the QCM with dissipation (QCM-D) technique in conjunction with SPR, atomic force microscopy (AFM), and computer simulations [5-12]. They found that the process of bilayer formation occurs in three successive steps (1) in the first stage, vesicles attach to the surface via inter molecular interactions (2) at a critical surface coverage, the vesicles start to rupture, fuse on the surface, and thus form bilayer islands coexisting with vesicles and uncovered substrate (3) eventually, a coherent bilayer is formed covering the entire surface. 

Here, planar lipid bilayers are prepared by a modification of the original technique described by McConnell et al. (1). First, small unilamellar vesicles are prepared from phospholipids and then... 

For the investigation of the properties of BLMs, electrical methods have been applied at the very beginning. In addition to the CV technique, other methods such as electrical impedance spectroscopy (EIS) have been applied. Shortly after the discovery of the BLM system, Hanai and Hay don reported the thickness measurement of a planar lipid bilayer using the impedance technique [1 - 3]. Their results are in accord with the value obtained on RBC, estimated by Fricke (see Eq. 1). The impedance technique, nowadays also known as EIS, has subsequently used by many others. The basis of the technique is that a small alternating current (AC) of known frequency and amplitude is applied to the system (e.g. a BLM). The resulting amplitude and phase difference that develop across the BLM are monitored. For a BLM of cross-sectional area (A), and thickness the ability of the BLM to conduct and to store electrical charges are described by the following ... 

Rappolt, M. Chapter two—Formation of curved membranes and membrane fusion processes studied by synchrotron X-ray-scattering techniques. Adv. Planar Lipid Bilayers... 

Artificial cell models have been developed to help understand the membrane fusion process. A common model that involves vesicles containing channel proteins that are driven by osmotic pressure to fuse with a planar lipid bilayer was reported. A protein-free model has also been used to demonstrate transient opening of fusion pores. " Liposomes have been described as artificial cells and have also been used to examine membrane fusion. - Recently, an electroinjection technique has been developed, which makes it possible to form lipid nanotubes and networks between liposome reservoirs. - Here, we briefly present two models, recent advances in the development of a liposome-lipid nanotube network as an artificial cell model that mimics the latter stages of exocytosis for cell study and fusion of vesicles inside liposomes with a DNA zipper. 

Supported lipid bilayers on planar silicon substrates have been formed using S-layer protein from B. coagulans E38/vl and from B. sphaericus CCM 2177 as support onto which l,2-dimyristoyl-OT-glycero-3-phosphocholine (DMPC) (pure or mixtures with 30% cholesterol) or DPPC bilayers were deposited by the Langmuir-Blodgett-technique (Pig. 

Ions and small molecules may be transported across cell membranes or lipid bilayers by artificial methods that employ either a carrier or channel mechanism. The former mechanism is worthy of brief investigation as it has several ramifications in the design of selectivity filters in artificial transmembrane channels. To date there are few examples where transmembrane studies have been carried out on artificial transporters. The channel mechanism is much more amenable to analysis by traditional biological techniques, such as planar bilayer and patch clamp methods, so perhaps it is not surprising that more work has been done to model transmembrane channels. 

The development of biophysical techniques to make possible measurements of single ion channels in membrane bilayers has been fundamental to the advances in the understanding of how natural ionophores, particularly ion channel proteins, operate at the molecular level. The two principal techniques are the planar lipid... 

Because of their advanced level of development, high sensitivity, and broad applicability, fluorescence spectroscopy with labeled LUVs and planar bilayer conductance experiments are the two techniques of choice to study synthetic transport systems. The broad applicability of the former also includes ion carriers, but it is extremely difficult to differentiate a carrier from a channel or pore mechanism by LUV experiments. However, the breadth and depth accessible with fluorogenic vesicles in a reliable user-friendly manner are unmatched by any other technique. Planar bilayer conductance experiments are restricted to ion channels and pores and are commonly accepted as substantial evidence for their existence. Exflemely informative, these fragile single-molecule experiments can be very difficult to execute and interpret. Another example for alternative techniques to analyze synthetic transport systems in LUVs is ion-selective electrodes. Conductance experiments in supported lipid bilayer membranes may be mentioned as well. Although these methods are less frequently used, they may be added to the repertoire of the supramolecular chemist. 

One of the early hopes was that the technique could be used to create ultrathin insulating layers for field effect transistors and other electronic devices. This application is, however, bedeviled by the presence of very small defects (pinholes) in the films. These defects can be obviated by using a material whose transition temperature is well below room temperature (at which, it is assumed, fabrication takes place), such as the phospholipids found in nature as the main amphiphilic components of the ubiquitous bilayer lipid membrane that surrounds cells and their internal organelles, but these molecules are not very robust and would not have the longevity required in typical electronics applications. Another attempted application has been the creation of planar optical waveguides, but it turned out to... 

Various planar membrane models have been developed, either for fundamental studies or for translational applications monolayers at the air-water interface, freestanding films in solution, solid supported membranes, and membranes on a porous solid support. Planar biomimetic membranes based on amphiphilic block copolymers are important artificial systems often used to mimic natural membranes. Their advantages, compared to artificial lipid membranes, are their improved stability and the possibility of chemically tailoring their structures. The simplest model of such a planar membrane is a monolayer at the air-water interface, formed when amphiphilic molecules are spread on water. As cell membrane models, it is more common to use free-standing membranes in which both sides of the membrane are accessible to water or buffer, and thus a bilayer is formed. The disadvantage of these two membrane models is the lack of stability, which can be overcome by the development of a solid supported membrane model. Characterization of such planar membranes can be challenging and several techniques, such as AFM, quartz crystal microbalance (QCM), infrared (IR) spectroscopy, confocal laser scan microscopy (CLSM), electrophoretic mobility, surface plasmon resonance (SPR), contact angle, ellipsometry, electrochemical impedance spectroscopy (EIS), patch clamp, or X-ray electron spectroscopy (XPS) have been used to characterize their... 

Planar bilayer lipid membranes (BLM) with diameters up to 2 mm separating two aqueous solutions, which are especially suitable for electrical measurements, can be formed by a variety of techniques. Spherical bilayer lipid membranes (liposomes) ranging from 200 A to 1 cm diameter can also be formed by numerous methods . A brief description of the BLM system only will be given here along with experimental setups. 

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